Color television



Dec- 3, 1942- P. c. GOLDMARK 2,304,081

COLOR TELEVI S ION Filed Sept. 7, 1940 4 Sheets-Sheet l BY b@ I, @wl

ATTO R N EYS Dec., 8, 1942. P. c. GOLDMARK COLOR TELEVIS ION Filed Sept. 7,4 1940 4 Sheets-Sheet 2 Dec. 8, 1942. Q GQLDMARK 2,304,081

COLOR TELEVIS ION Filed Sept. 7, 1940 4 Sheets-Sheet 3 1 N v E N To R feier C a/dwaf @ma il?,

ATTORN EYS De S, i942- P. c. GOLDMRK 2,304,081

COLOR TELEVIS ION Filed Sept. 7, 1940 4 Sheets-Sheet 4 INVENTOR gg A'ToRNEYs Mg' Patented Dec. 8, 1942 UNITED STATES PATENT OFFICE COLOR TELEVISION Peter C. Goldmark, New York, N. Y., assignor to Columbia Broadcasting System, Inc., New York, N. Y., a corporation of New York Application September 7, 1940, Serial No. 355,839

(Cl. Nil-5.4)

Claims.

This invention relates to television, especially to television in natural colors. The invention is particularly directed to the combination with a transmitting or receiving scanning device of a rotatable color filter disk having segments of novel design.

It has heretofore been suggested to achieve colored television by employing at the receiver a cathode-ray tube and a disk having red, green and blue lter sectors revolving in front of the tube. At the transmitter, a similar disk is arranged in front of the scanning device and the two disks are rotated in synchronism. The entire object field is scanned successively through red, green and blue filters and the signals transmitted to the receiver. At the receiver, the disk is phased with respect to the incoming signals so that when an image corresponding to the red portion of the object field is reproduced on the fluorescent screen of the cathode-ray tube, the screen will be viewed through the red filter, and similarly for the green and blue filters.

In such instances it has been customary to employ filter disks in which the individual sectors are bounded by straight radial lines. The disk is commonly positioned so that the filters rotate in the direction of the low-frequency or eld scansion. The dimensions of the disk must be so chosen that complete scanning lines are progressively covered by a given filter segment in such a manner that as the scanning proceeds the line being scanned will always be obscured by the proper color filter. At the receiver it is desirable to employ a tube having considerable after-glow, so as to increase the amount of light emitted. In such case, all lines of the reproduced image should remain obscured by a given filter sector for a substantial interval after they are scanned.

Because of these requirements for proper operation such filter disks employing sectors are required to be of rather large diameter, or the sectors must extend over a wide angle, thereby allowing space for only a few sectors and requiring the disk to rotate at a relatively high speed. Bath large diameter and high speed are of course obiectionable. This is particularly true of receivers, where economy of space, and safety and reliability of operation are exceedingly important, and where image areas of considerable magnitude are common.

In accordance with the present invention, a disk is provided in which the filter segments are designed so that one or both of their outwardlyextending edges l leading and trailing edges),

re non-radial. In general, the outer portion of one or both of the outwardly-extending edges is displaced with respect to the inner portion of that edge by a substantial central angle. Also, in general, the filter segments extend over central angles which are greater than the angular spacing of the filter segments around the disk. Usually one of the outwardly extending edges of a segment is convex and the other concave. The outwardly extending edges are usually curved, but they can in some cases be formed by straight lines as described hereinafter. One or more of these features can be incorporated in the design of the disk, depending on the use contemplated.

Filter disks constructed in accordance with the invention possess considerable advantage over disks heretofore constructed, the particular advantages depending on the use of the disk and the particular construction thereof. Smaller disks, or disks containing more segments and hence rotatable at lower speeds, or both, may be employed. Also advantages pertaining to the period of afterglow, economy of filter material, less driving power, etc., may be obtained. These advantages are of especial importance in the case of receiver tubes, particularly those with large image areas, but may also be of advantage for transmitters also.

In one embodiment hereinafter described the leading edge progressively covers complete scanning lines at substantially the same rate as that at which the lines are scanned. Other embodiments are modifications designed to give satisfactory results for particular uses. The principles of the designs are discussed at considerable length, and it will be apparent that many further specific designs may be made Within the scope of the invention.

The invention will be more readily understood by the following detailed description, taken in conjunction with the drawings which illustrate several specific embodiments.

In the drawings:

Fig. 1 illustrates a color television transmission system;

Fig. 2 illustrates a color television receiving system;

Fig. 3 illustrates a form of color filter disk constructed in accordance with the invention;

Figs. 4 and 5 illustrate one design of filter segments and the manner of constructing same;

Fig. 6 illustrates a modified design and the manner of constructing same;

Fig. 7 illustrates another modification and manner of constructing same;

Figs. 8 and 9 illustrate a still further embodiment and manner of constructing same; and

Fig. 10 is a detail illustrating certain angles.

Referring to Fig. l, the light from a projection source III. which may be any suitable light source such as an arc or a projection lamp, is condensed by suitable means such as condenser lenses Il onto a picture gate I2. In thev path of the light is positioned a heat filter I3 which is advantageously of the water type, so as to effectively cut of heat waves from the picture gate. A color lllter disk Il, rotatable about an axis I5 by motor 20, is interposed in the path of light to the picture gate. The lter disk is preferably mounted parallel to the plane of the gate and fairly close thereto. The disk may of course be placed on the opposite side of the picture gate from that shown, and in either position will serve to obscure an image at the gate from the point of view of the scanning device.

A projection lens I6 is employed to project an image in the gate l2 to the photoelectric cathode I1 of the scanning tube I 8, here shown as a tube of the Farnsworth Image Dissector type. Between the picture gate I2 and the projection lens I6 is interposed an infrared filter I9. This: filter, in conjunction with the water lter I3 effectively prevents infrared rays from reaching the image dissector. Such a filter is desirable since photoelectric surfaces are commonly sensitive to infrared, and therefore it is necessary to eliminate infrared rays in order to obtain signals which correctly represent the various primary colors of an object eld in the gate I2. Infrared could of course be cut olf at other points in the path of light to the scanner.

Although a scanning tube of the image dissector type is illustrated, it will be understood that this is shown only by way of example, and that other suitable forms of scanning devices can be employed. In particular, nonstorage scanning devices are desirable, such as scanning disksetc. In the case of a scanning disk, the filter disk might be placed close to the plane thereof, if desired. It will be understood that in Fig. l the image area on the cathode I'I is conjugate to the image area in the gate I2, and that therefore either area. may be considered a scanning area as the term is used herein.

The picture gate I2 is illustrated as of the type designed to accommodate color slides of, for example, the Kodachrome type. Instead of slides, the apparatus may of course be designed for use with motion picture film. The use of an intermittent film projector is obvious, the lm remaining stationary during scanning and being moved from one frame to the next during the blanking period. Continuously moving lm scanners may also be employed. In general, it is advantageous to place the filter disk as near the area or field being scanned as possible.

In Fig. 1 the usual vertical and horizontal de- Ilecting coils of the image dissector I8 have been omitted for simplicity of illustration, but will be understood to be employed. The motor 2li, which drives the lter disk I4, is synchronized with the low-frequency deflection. It is contemplated that the lter segments will successively traverse the scanning area at the same frequency as the lowfrequency or field scansion. In the case of noninterlaccd scansion all lines of the image area will be scanned while the area is obscured by a single filter segment. In interlaced scansion, it is contemplated that the area will be obscured by a single segment during only one eld scansion,

during which only one set of lines are scanned, in accordance with the system disclosed in my copending application Serial No. 355,840, led September 7, 1940. It will be understood, however, that the present invention is not limited to any particular system of scanning and that the design of the nlter segments may be adapted to the particular system employed.

Referring to Fig. 2, a television receiving tube 2l of the cathode-ray type is employed. In front of the tube is positioned a. color lter disk 22, mounted to be rotated about axis 23 by motor 2l. The filter disk is advantageously placed as close as possible to the face of the cathode ray tube and parallel therewith. Suitable receiving circuits and deilecting means, not shown, will of course be employed. Motor 2l is synchronized and phased with the received signals so that the image area on the end of the cathode-ray tube is obscured by the red filter when an image corresponding to the red part of the transmitted picture is being reproduced, and similarly for green and blue. It is contemplated that both transmitting and receiving disks will he driven at uniform speed.

Although the invention is particularly useful with a cathode-ray receiving tube, particularly of a large size, other forms of receiving devices such as, for example, scanning disks may be employedr if desired. In any case, the disk will ordinarily be positioned to cover the scanning area so that images of proper color will be presented to view. Although transmission and reproduction in three primary colors is contemplated, a dilerent number of colors could be employed if desired.

Fig. 3 illustrates a type of disk, constructed in accordance with the invention, which may be used for the transmitting disk I4 and the receiving disk 22. The disk has a plurality of segments of different light transmission characteristics, usually color filters, spaced around the disk. The transmitting and receiving lter disks may be of similar design, but will ordinarily not be identical since the size of the image at transmitter and receiver will ordinarily be dilerent. Of course, it is not necessary that similar filter disks be employed at both transmitter and receiver. The transmitter illustrated in Fig. 1 is designed to provide a signal in which successful field scansions yield signals corresponding to different primary colors. In the receiver of Fig. 2, each field scansion is reproduced as an image on the end of the cathode-ray tube, and this image is viewed through the lter of the proper color. Obviously, the receiver of Fig. 2 may be used with any signals of proper type, whether produced by the transmitter shown in Fig. 1 or any other type of transmitter. Similarly, other types of receivers could be used with the signals transmitted with the apparatus of Fig. l.

Referring now to Figs. 4 and 5, a method of designing the lter segments will be described. The rectangle 3l represents the area of the image to be obscured by the color filter disk. For example, this may be the area oi the image in gate I2 of the transmitter or on the end of the cathode-ray tube 2l at the receiver. The axis 32 of the lter disk is illustrated as positioned on an extension of a diagonal of the image area 3l. While this is considered advantageous, it is not essential. The axis may be located elsewhere if desired. In order to make the diameter of the disk small, the axis is preferably located quite close to the image area, the design of the segments in accordance with the invention making this feasible. i

'Ihe disk shown is designed for 6 filter segments/consisting of two sets of red, green and blue filters such as ordinarily used in color reproduction. For such a disk, a single iield scansionr (interlaced or non-interlaced) of the image area 3| takes place while the disk rotates through an angle of 60. Part of this iield-scansion period is devoted to blanking, so as to permit the cathode ray to return from the end of the image area to the beginning thereof for the next scansion. According to present standards, the blanking period is 10% of the ield-scansion period so that the disk rotates through 6 during the blanking period.

In Fig. 4, assume that the horizontal line 33 represents the beginning of a blanking period. The line 34, at an angle of 6 with respect to line 33, represents the end of the blanking period. Similarly, line 35, making an angle of 60.

with respect to line 33, and 54 with respect to line 34, represents the end of a eld-scansion period. The arc of the circle between lines 34 and 35 is divided into eight equal parts as indicated. Similarly, the lateral edges of the image area 3| 'are divided into eight equal parts. Thus, while the disk turns through an angle from line 34 to point I on the circumference, the scanning beam will scan the area from line Il" to line of image area 3|.

To construct one of the outwardly extending curves bounding the filter segments, take a sheet of tracing paper, draw on it a line A (Fig. 5") and mark pivot point 32'. Pivot the tracing sheet to the sheet containing the image area 3|, with pivot points 32 and 32 coinciding. Align line A with line 3d and mark on the tracing sheet the points U'L and 0"L which lie over 4points 0 and 0 of Figi 4. Rotate the tracing sheet until line A passes through point of Fig. 4 and mark points lr. and |1. on the translucent sheet. Rotate the tracing sheet until line A passes through point 2 of Fig. 4 and mark points 21. and 2"L. Continue until points 8L and 8r. lying over 8' and 8" of Fig. 4 have been marked on the tracing sheet. This procedure will give the points 0L-81., 0"L-8L shown in Fig. 5. Draw a smooth curve through these points as shown.

The curve of Fig. 5, when repeated at 60 intervals around the pivot point will yield the segments R, G, B, R', G', B', shown in Fig. 4.

'I'he operation of the lter disk of Fig. 4 is apparent from the foregoing. The image area 3| is scanned in horizontal lines beginning at the top and progressing to the bottom at a uniform speed. Assume that when the leading edge of lter segment R is in the position shown by the full line (that is, the leading edge passes through the points 0 and 0"), the scanning of line IJ 0 takes place. As the lines are progressively scanned in a downward direction, the uniform rotation of the disk causes lter segment R to obscure complete lines at substantially the same rate as that at which they are scanned. Thus, when the scanning beam reaches line the filter segment R has reached the same line, and similarly down the image area. The dotted curves show the positions of the leading edge of iilter segment R as the disk rotates.

As the scanning beam reaches the last line 8" 8', the leading edge of lter segment R 'also reaches it. During the next 6 of rotation, the

scanning beam returns to the top of the'scanning area. The next neld scansion then begins. filter segment C+ occupying the same position that segment R occupies in Fig. 4, and scanning proceeds in the manner described. The image area is thus successively obscured by successive filter segments at field-scanning frequency.

It will be observed that although the angular spacing of the filter segments (that is, the angle between corresponding points of adjacent segments) is 60, each filter segment extends over (or subtends) a central angle S of about 123, as indicated in Fig. 4. Also, the central angle L between the inner portion of the leading edge and the outer portion thereof is about 621/2". The central angle between the inner and outer portions of the trailing edge is the same, since the adjacent segments are contiguous in Fig. 4. The leading edge is convex and the trailing edge is concave. Also, the points of intersection of the leading edge (and also the trailing edge) with the lateral edges of the scanning area 3| move down the lateral edges at the same speed as the scanning beam.

If the segments were sectors, as heretofore suggested, the angle over which the segments extend could not be greater than the angular spacing, and a disk considerably larger in diameter would be required to give the same results.

It, of course, is not necessary that the disk be phased with respect to the scanning beam so that the leading edge obscures each complete scanning line at the exactl instant that lixe 2s being scanned. The color disk may be phased so that the leading edge is considerably in ad- 'vance of the scanning beam, if desired. In receiving tubes possessing after-glow, the advance in phase of the disk should ordinarily not be so great that objectionable after-glow would persist after the next illter segment comes into operation.

Fig. 6 illustrates the manner in which the filter segments of Fig. 4 may be modied to conserve lter area. The leading edge 36 is constructed in the manner described in connection with Figs; 4 and 5. In Fig. 6, straight lines have been drawn between respective pairs of points 01. ||"L, |L |r.-8'i. 8"L. Assuming that the disk is phased with respect to the scanning beam so that scan ning begins at the instant line 0L 0L coincides with the top line of the picture, the subsequent lines I'r. |"L, etc. indicates the lines of the lter segment which coincide with the lines of the image area being scanned as the disk rotates.

In a transmitting tube of the non-storage type, it is necessary that each line of the image area be obscured by the filter` segment at only the instant that the line is being scanned. Thus only the portion of the iilter segment covered by lines 01. 0"r.8r. 8"L is strictly necessary for scanning with a non-storage transmitting system. However, such a iilter segment would require very accurate phasing of the disk with respect to the scanning beam. Therefore a wider lter segment would ordinarily be employed so as to make phasing less critical. For example, if the filter segment is shaped with a leading edge 36 as shown and a trailing edge 3l as shown, the disk may be shifted Within an angle of about l31/2 and still preserve the correct relationship between the disk and scanning beam.

The manner in which the trailing edge 31 is constructed for this conditions is as follows: As described above, the leading edge 36 is constructed by placing a sheet of tracing paper over Fig. 4 and fastening it' with a thumb tack to rotate about the axis of Fig. 4. Line A is positioned to coincide with line 34 of Fig. 4, and line 01. Il"r. drawn. Line A is then rotated successively through points I, 2, 3, etc. on the circumference of the circle of Fig. 4, and corresponding lines Ir. I"r., 2'r. 2"r., etc. drawn on the tracing paper of Fig. 6. The leading edge 36 is then obtained by drawing a smooth curve throughthe points Iir., |r.8x. on the tracing paper. It will be observed that a notch 38 may be cut in the leading edge of the filter segment without affecting the scanning.

'I'he trailing edge 3'I is constructed by rotating line A to coincide with point 2 on the circumference of Fig. 4, and then drawing on the tracing paper a line Il'r 0r coinciding with line Il' Ill of Fig. 4. When line A has been rotated from line 34 to point 2, the angle of rotation is 131/2. Therefore, if the filter segment is made large enough to include the area between line 'r. li"r. and line T 0"'r, the top line of the scanning area 3| (Fig. 4) will be obscured by the lter segment throughout 131/ of rotation.

Additional lines are drawn by rotating line A to point 3 of Fig. 4 and tracing line I'r I"'r over line I I of Fig. 4, and so on until line A coincides with point 8 of Fig. 4 and corresponding line 6rj6"r is drawn. Line A is then rotated through two additional equal angles indicated by points 9 and I0 in Fig. 4, and lines 'Ir 1"T and 8'1' 8'1- coinciding with lines 1' 1 and 8 8" of Fig. 4 traced. The various lines traced are indicated in Fig. 6, the first and last lines being numbered DT 0"-1- and 8'r 8"'r. The trailing edge 31 is then drawn through the locus formed by the lines, as shown. The filter segment thus constructed will obscure the entire length of each line of scanning area 3| of Fig. 4 as that line is scanned, even though the phase of the disk with respect to the scanning beam is Varied through 131/2. Thus, if the disk is phased so that when the scanning beam is on line 0 of Fig. 4, some part of the area of the filter segment lying between lines 01. Il"r. and O'r 0r is over line D' 0", successive lines will always be obscured as the scanning beam reaches them.

In Fig. 6, the central angle L over/which the leading edge of the filter segment extends is ap-v proximately 62 1/2". Also, the central angle S subtended by the entire filter segment is approximately 761/2". Six of these segments may be spaced around the disk with equal angular spacings, thereby making the angular spacings i60".v

If desired, instead of forming the outlines of the filter segments with smooth curves, as shown in full lines, the outline could be formed with straight lines, as indicated by dotted lines 39, '39', 39". The leading edge 39, 39" is still convex', although formed with an angle instead of a smooth curve. Such an outline includes a considerable amount of unnecessary filter material and hence represents waste, but may be employed if desired.

adapted for use with a cathode-ray receiver tube possessing considerable after-glow. In Fig. 4 it will be observed that as the disk rotates past the image area 3| in a counter-clockwise direction, each line of the image area is obscured by the red filter R until the leading edge of the next green iilter segment G begins to lobscure that line. In Figs. 4 and 5, assuming scanning of the top line of the image area to begin when the line A coincides with line 34. the full length of the top line remains obscured by the red filter throughout an angie of approximately 32, or slightly more than half the total field-scansion period. The outer portions of the image area will remain obscured throughout a greater angle. Therefore, a portion of the filter may be cut of! at the outer edge and still cover the outer elemental areas of the image for as long a period as the inner elemental areas. which may be'particularly important for receivers employing large cathode-ray tubes.

Fig. "l illustrates such a construction. The leading edge 38 of segment R is constructed in the manner hereinbefore described, using A as a reference line. The curve is repeated at 80 intervals to form the leading edges of segments G and B. The trailing edge is constructed in a manner analogous to that described in connection with Fig. 6. 'I'he tracing paper on which the leading edge of R is constructed is rotated until the leading edge of the next filter segment G touches the top of image area 3| of Fig. 4. A new reference line A' is then drawn to coincide with line v31| of Fig. 4. The angle between line A' and A represents the maximum angle through which a given segment of the lter disk will obscure the entire length of line 0' 0" of Fig. 4. In this position of the tracing paper, line 'a W'n is traced. Line A is then rotated through points I, 2, 3, etc. successively, and corresponding lines traced over lines I' I", 2' 2", etc. of Fig. 4. These However. it should be noted that sectorsformed by radial lines cannot be employed, since the central angle through which the illter segment extends is greater than the angular separation of filter segments. Thus the disk of Fig. 6 may be smaller than'a disk with sector segments.

With a larger disk, the pattern of ,lines in Fig. 6 might fall entirely within a 60 central angle. In such case the shape shown in full lines would possess the advantage of requiring much less filter material than sectors formed by radial lines.

Fig. '1 illustrates a filter segment particularly lines are shown in Fig. '7, the first and last lines being numbered Il'a Iifn and 8a 8"a. The trailing edge 40 may then be drawn through the locus determined by these lines.

When so constructed, the outer portions of the lter segments will cover complete scanned lines for the same length of time after scanning as the inner portions, hut no longer, and the areas 4I represent saving in filter material. Areas 4| are preferably made opaque.

In the foregoing discussion of Figs. 4 to 7, the terms leading edge and trailing edge" have been employed, the disk being assumed to rotate in a counter-clockwise direction. However, when the segments have been constructed as described and the disk made accordingly, the disk may be Vrotated in either direction with substantially the same results. With clockwise rotation, scanning should begin'at the bottom of the scanning area 3| (Fig. 4) and the'phase of the disk with respect to the scanning beam should be adjusted so that the lines being scanned are covered by the respective lter segment at the time of scanning.

Figs. 8 and 9 illustrate another embodiment which diiers somewhat from those described previously. The axis of rotation is placed at the bottom of the picture, rather than at the top, and is placed on an extension of -the lower edge of the scanning area instead of on a. diagonal. It is believed advantageous to position the axis within the angle included by the projections of two adjacent sides of the scanning area (angles C of Fig. 10) or fairly close thereto, that is, within substantially that angle. If desired, however,

This results in economy of filter material,

the axis may be ning area.

In Figs. 8 and 9, the disk is composed of six outwardly-extending lter segments R, G, B, R', G', B spaced evenly around the disk. The disk is assumed to rotate in a clockwise direction and scanning of the image area 3| is from bottom to top. Between the trailing edge 46 of one lter segment and the leading edge 41 of the next lter segment is an irregular section 4B not occupied by lter material. The shape of area 48, and hence the amount of illter material saved, may be determined in the manner described in connection with Fig. 7.

Lines '1. 0"n-8L 8"L of Fig. 9 are traced over lines 0' 0"-8' 8" of Fig. 8, using lineA as a reference line, in the manner described hereinbefore. Rotation of line A is in a clockwise direction, the reverse of previous gures, since scanning is from bottom to top. Leading edge 41 is drawn to include the traced lines and is repeated at 60 intervals. The tracing paper of Fig. 9 is then rotated until the leading edge of the next segment just touches the bottom of the scanning area 3|, and line A traced over line 34 of Fig. 8. This condition is illustrated in Fig. 8. Lines (lR [Wa- 8'iz 8"R are then traced, using line A' as a reference. This procedure is similar to that described in connection with Fig. 7, and makes the interval any given scanned line is covered after scanning the same for outer and inner portions of the filter segments.

The outline of the lter segment is drawn to include the traced lines. Some excess area is contained in the leading and trailing portions of the segment, since the size of commercially available sheets of lter material made it unnecessary to cut the area down further. The shape of the segment is such as to allow some margin of inaccuracy of adjustment, etc. It will be noted that the leading and trailing edges extend over or subtend central angles L and T of 441/2 and 251/2" respectively, and the segment extends over an angle S of 861/ The edges 46, opposed to edges 41, are cut away as a result of the construction so as to accommodate the convex portions of the edges 41. Edge 41 of the outline shown closely follows the ends of the traced lines from points ZL to 8'L. Therefore, as the disk placed elsewhere about the scanturns through equal angles, the point of interg section between edge 41 and the projection of the lateral edge of area 3| nearer the axis 32 onto the plane of the disk moves along the lateral edge equal distances for a major part of the lateral e e.

d'he disk may be rotated in counterclockwise direction, if desired, by scanning the area from top to bottom and adjusting the phase of the disk with respect to the scanning beam, as mentioned hereinbeiore.

In the foregoing the disks have been designed for use with a scanning beam which moves uniformly in a vertical direction, as is customary at the present time. For non-uniform movements the principlesV of design disclosed may still be applied by rotating the tracing paper the correct amount for a given displacement of the scanning beam. Disks with six segments have been specically described, since that yields a disk of relatively small diameter rotating at a speed which is not excessive. Diierent numbers of segments may of course be employed if desired, the angle through which the disk rotates for a single eld scansion being changed accordingly.

The disks speciiically described have segments of the same size and shape arranged at equal angular distances around the disk. If required or desired for any particular use, differently shaped segments and non-uniform spacing may be employed.

If it is desired to use spokes or other solid members between lter segments tne segments may be altered accordingly. Preferably the spokes should not cut into the area covered by the traced lines, but minor incursions may be permissible in many cases.

The particular filter segment patterns described are of course given for purposes of illustiation only, and many modications thereof may be made within the spirit and scope of the invention. Also, the uses oi the filter disks are obviously not limited to the particular apparatus described herein.

I claim:

l. In television apparatus, in combination with means for scanning an entire image area from one limiting boundary to the other by complete parallel lines extending fully across said area and advancing progressively at uniform speed, a rotatable disk having similar sets of a plurality of non-radial segments of diierent, light transmission characteristics spaced around the disk at selected angular spacings, each of said segments extending over central angles substantially greater than said angular spacings, said disk being positioned closely adjacent said image area so that said segments in rotating succesand proportloned witn respect to the full length of the said scanning lines and adapted to progressively obscure the entirety of each successive complete scanning line at substantially the same said uniform speed at which the lines are advanced in scanning.

2. In color television apparatus, in combination with means for scanning an entire substantially rectangular image area in one direction at linescanning frequency and in a substantially perpendicular direction at eld-scanning frequency by complete parallel lines extending entirely across said area and advancing progressively at uniform speed, a color lter disk having a plurality of outwardly extending non-radial filter segments spaced around said disk at selected angular spacings, said disk being rotatable about an axis outside of said image area and positioned adjacent thereto so that rotation thereof ing one outwardly extending edge convex over at least a portion thereof near the axis, the opposed outwardly extending edges of adjacent segments to accommodate said convex for rotating said disk at a speed such that filter segments traverse the image area at substantially field-scanning frequency, said lter segments being jections of complete scanning lines of said image perpendicular direction at eld-scanning frequency by complete parallel lines extending entirely across said area and advancing progressively at uniform speed, a color filter disk having a. plurality of outwardly extending non-radial filter segments spaced around said disk at selected angular spacings, said disk being rotatable about an axis outside of said image area and positioned adjacent thereto so that rotation thereof causes said image area to be successively obscured by successive filter segments, said filter segments extending over respective central :angles greater than said angular spacings, and means for rotating said disk at a speed such that filter segments traverse the image area at substantially field-scanning frequency, the other portion of the trailing edges of the lter segments being cut off so that complete lines at the beginning and end of a field scansion period remain obscured by a filter segment for substantially the same length of time after the scanning of the respective complete lines.

4. In color television apparatus, in combination with means for scanning an entire substantially rectangular image area in one direction at line-scanning frequency and in a substantially perpendicular direction at field-scanning frequency by complete parallel lines extending entirely across said area and advancing progressively at uniform speed, a color filter disk having a plurality of outwardly-extending non-radial lter segments spaced around said disk, said disk being rotatable about an axis outside of said image area and positioned adjacent thereto so that rotation thereof causes said image area to be successively obscured by successive filter segments, and means for rotating said disk at a speed such that filter segments traverse the image area at substantially field-scanning frequency, said lter segments being shaped to include the projections of complete scanning lines of said image area on the lter disk when the lines are scanned during their respective eld scanning periods and the outwardly extending edges of each of said filter segments being respectively substantially convex and substantially concave.

5. In color television apparatus, in combination with means for scanning a substantially rectangular image area in one direction at linescanning frequency and in a substantially perpendicular direction at field-scanning frequency by complete parallel lines extending entirely across said area and advancing progressively at uniform speed, a color filter disk rotatable about an axis outside of said image area in a plane substantially parallel to the image area and near thereto, said disk having a diameter sufiicient to include said image area, means for rotating said disk at substantially uniform speed.. said disk having a plurality of outwardly-extending differently-colored non-radial filter segments spaced around the disk, the leading edge of each of said plurality of filter segments being of such curvature that successive complete lines of the image area are exposed through the filter segment at substantially the same rate as that at which the lines are scanned.

6. In color television apparatus, in combination with means for scanning an entire substantially rectangular image area in one direction at line-scanning frequency and in a substantially perpendicular direction at eld-scanning frequency by complete parallel lines extending entirely across said area and advancing progressively at uniform speed, a color filter disk rotatable about an axis outside of said image area and having a diameter suicient to include said 'l5 image area, said disk having a plurality of outwardly-extending differently-colored non-radial filter segments spaced around the disk, one outwardly-extending edge of each of said plurality of filter segments having a curvature such that the point of intersection of the lateral edge of the image area nearer the axis with the projection of said one edge onto the image area moves along the lateral edge substantially equal distances for equal angular movements of the disk for at least a substantial portion of the lateral edge.

7. In color television apparatus, in combination with means for scanning an entire substantially rectangular image area in one direction at line-scanning frequency and in a substantially perpendicular direction at field-scanning frequency by complete parallel lines extending entirely across said area and advancing progressively at uniform speed, a disk rotatable in a plane near said image area and substantially parallel thereto, the axis of rotation of said disk being within substantially the angle included by the projections of two adjacent sides of the said rectangular image area, said disk having a diameter sufficient to include said image area and having a. plurality of differently-colored outwardly-extending lter segments spaced around said disk at selected angular spacings, means for rotating the disk at a uniform speed in synchronism with the fleld scansion .such that said filter segments traverse the image area. at substantially field-scansion frequency, said lter segments having at least one outwardly-extending edge non-radial and extending over respective central angles greater than the angular spacing thereof and being shaped to include the projections of complete scanning lines of said image area on the lter disk when the lines are scanned during the respective field-scanning periods.

8. In color-television receiving apparatus the combination with a cathode-ray receiving tube having a luminous screen of a magnitude sufficient to reproduce images of substantial area for direct viewing, and means for scanning the entirety of said image area by complete substantially horizontal parallel lines extending fully thereacross and advancing progressively at uniform speed, of a color-filter disk rotatable about an axis disposed adjacent said tube Within the angle included by the projections of two adjacent sides of said area, and having similar sets of a plurality of non-radial segments of dierent color filters spaced around the disk at selected angular spacings, each of said color-lter segments extending over a central angle substantially greater than said angular spacing, said disk being positioned closely adjacent said screen in substantially parallel relation so that the color-filter segments in rotating successively traverse the image area, the leading edge portions of each of said color-filter segments being similarly convex and proportioned with respect to the full length of the said scanning lines and adapted to obscure each successive complete scanning line progressively at substantially the same said uniform speed at which the lines are advanced in scanning.

9. In color-television apparatus, the combination with means for scanning an entire image area from one limiting boundary to the other thereof by complete parallel lines extending fully across said area. and advancing progressively at uniform speed, of a color-filter disk rotatable about an axis disposed within the angle included by the projections of two adjacent sides of the boundary of said area and having substantially similar sets of a plurality of non-radial segments of diierent color lters spaced around the disk at selected angular spacings, each of said color-filter segments extending over a central angle substantially greater than said angular spacings, said disk being positioned closely adjacent said image area so that the said colorlter segments in rotating successively traverse the image area, the leading edge portions of each of said color-iilter segments being similarly convex and proportioned with respect to the full length of the said scanning lines and being adapted to obscure the entirety of each successive conplete scanning line progressively at substantially the same said uniform speed at which the lines are advanced in scanning.

10. In color-television apparatus the combination with means for scanning an entire substantially rectangular image area in one direction at line scanning frequency, and in a substantially perpendicular direction at eld scanning frequency by complete parallel lines extending entirely across said area and advancing progressively at uniform speed, of a rotatable colorilter disk having two similar sets of three different color filters arranged in like shaped segments spaced around said disk at selected angular spacings and disposed in a plane parallel and adjacent said image area, the axis of rotation of said disk lying within substantially the angle included by projections of two adjacent sides of the said rectangular image area, means for rotating said disk in synchronism with the field scansion so that the lter segments in rotation successively traverse the entire image area at substantially said eld scansion frequency, each of said color-filter segments extending over a central angle substantially greater than said angular spacing and having one edge portion convex and proportioned with respect to the full length of said complete scanning lines so as to include the projections of the complete scanning lines of said image area during the respective scanning periods.

PETER C. GOLDMARK.

CERTIFICATE CF CORRECTION.

Patent No. 2,5ol;,o81. December 8, 19142.

. PETER c. GCLDMARK.

It is hereby certified that error appea-rs in the printed specification of the above numbered `patent requiring correction as follows: Page 5, second column, line 75, for "conditions" read -condition; age 6, first column,l line l5, claim 5, for "other" read -outer-; and that the said Letters Patent should be read with this correction therein that the same may confonn tothe record of the case in the Patent Office.

sighed and sealed this and day of February, A. D. 1915.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

